1. Field of the Invention
The present invention relates to a power transmitting apparatus for a hybrid vehicle and a method of controlling such a power transmitting apparatus.
2. Description of the Related Art
There is known a power transmitting apparatus for a hybrid vehicle which has two power distributors and two motors that can operate in both propulsive and regenerative modes. For example, reference should be made to xe2x80x9cBasic configuration of a parallel differential structured electric transmission system for hybrid electric vehiclesxe2x80x9d and xe2x80x9cCharacteristic evaluation of a parallel differential structured electric transmission system for hybrid electric vehiclesxe2x80x9d, Society of Automotive Engineers of Japan, Inc. Convention Preprint No. 2-00, May 2000.
A conceptual arrangement of the known power transmitting apparatus is shown in FIG. 6 of the accompanying drawings.
In the power transmitting apparatus, the rotational drive power from an output shaft 100a of an engine 100 is distributed and transmitted to input shafts 101a, 102a of respective two power distributors 101, 102 through gears, not shown. The power distributors 101, 102 comprise differential gear mechanisms or planetary gear mechanisms, and have two output shafts 101b, 101c and two output shafts 102b, 102c, respectively. The power distributors 101, 102 operate to generate a torque at a constant speed reduction ratio on their two output shafts regardless of the difference between the rotational speeds of the output shafts.
The output shafts 101b, 102b of the power distributors 101, 102 are connected to a common power output shaft 105 by respective rotation transmitting mechanisms 103, 104 which have different speed reduction ratios xcex1, xcex2 (xcex1, xcex2). The other output shafts 101c, 102c of the power distributors 101, 102 are connected to respective rotatable shafts 106a, 107a of motors 106, 107. The common power output shaft 105 is connected to the axle of drive wheels of a vehicle (hybrid vehicle), not shown. More precisely, the speed reduction ratios xcex1, xcex2 represent speed reduction ratios including those of the power distributors 101, 102. For illustrative purposes, however, the speed reduction ratios of the power distributors 101, 102 are herein assumed to be xe2x80x9c1xe2x80x9d.
When the engine 100 is operated and the motors 106, 107 are controlled to operate in propulsive and regenerative modes, respectively, to equalize the electric power consumed by the motor 106 with the electric power generated by the motor 107, part of the mechanical energy produced by the output shaft 100a of the engine 100 is converted into electric energy by the motor 107, and the electric energy is then converted back into mechanical energy by the motor 106. The mechanical energy produced by the motor 106 is transmitted to the power output shaft 105. The remainder of the mechanical energy from the engine 100 is mechanically transmitted to the power output shaft 105 without going through the motors 106, 107.
Since equilibrium is maintained between the energy consumed by the motor 106 and the energy generated by the motor 107 (it is assumed that energy losses caused by the motors 106, 107 are ignored), a torque Te produced by the output shaft 100a, i.e., a torque as a load on the engine 100, and a torque Tv transmitted to the power output shaft 105 are related to each other as indicated by the following equation (1):
Tv=(xcfx89e/xcfx89v)xc2x7Texe2x80x83xe2x80x83(1)
where xcfx89e represents the rotational speed of the output shaft 100a and xcfx89v the rotational speed of the power output shaft 105. Therefore, xcfx89e/xcfx89v represents a speed reduction ratio for transmitting the rotation from the output shaft 100a to the power output shaft 105.
The speed reduction ratio xcfx89e/xcfx89v between the output shaft 100a and the power output shaft 105 can be changed to any speed reduction ratio between the speed reduction ratio xcex1 of the rotation transmitting mechanism 103 and the speed reduction ratio xcex2 of the rotation transmitting mechanism 104 by controlling the torques generated at the motors 106, 107.
Consequently, when the vehicle is propelled by the engine 100 as a propulsion source, the speed reduction ratio xcfx89e/xcfx89v between the output shaft 100a and the power output shaft 105, i.e., a transmission ratio, can continuously be changed by controlling the torques of the motors 106, 107 while equalizing the electric power consumed by the motor 106 and the electric power generated by the motor 107 with each other. The power transmitting apparatus thus serves as an electric continuously variable transmission system for transmitting the output of the engine 1 to the power output shaft 105 to propel the vehicle, without the need for a mechanical transmission such as a pulley and belt type CVT or the like.
Another known electric continuously variable transmission system comprises a power transmitting apparatus having one power distributor and two motors. This electric continuously variable transmission system requires the motors to generate a greater torque than the power transmitting apparatus shown in FIG. 6 in its operation for continuously variable transmission. Consequently, the electric continuously variable transmission system is disadvantageous in that it needs large-capacity motors and their drive circuits and tends to cause an energy loss because more energy is transmitted from engine via the motors to the axle.
With the power transmitting apparatus shown in FIG. 6, if the torques of the motors 106, 107 are represented respectively by T1, T2, then in the state of equilibrium, the torque Te of the output shaft 100a, i.e., the torque as the load on the engine 100, and the torque Tv of the power output shaft 105 are related to each other according to the following equations (2), (3) (it is assumed that each of the power distributors 101, 102 comprises a differential gear mechanism):
Te/2=T1+T2xe2x80x83xe2x80x83(2)
Tv=xcex1xc2x7T1+xcex2T2xe2x80x83xe2x80x83(3)
By controlling the torques T1, T2 of the motors 106, 106, it is possible to impart a desired load torque Te to the output shaft 100a of the engine 100 and to generate a desired torque Tv on the power output shaft 105. The torques T1, T2 of the motors 106, 107 are controlled to cause the load torque Te on the output shaft 100a to become xe2x80x9c0xe2x80x9d, and a torque is generated on the power output shaft 105 to propel the vehicle, thereby holding the engine 100 at rest and propelling the vehicle with the drive power from the motor (EV mode=electric vehicle mode). In order to cause the load torque Te on the output shaft 100a to become xe2x80x9c0xe2x80x9d, the motors 106, 107 are operated in the propulsive mode and the regenerative mode, respectively, and part of the propulsive torque of the motor 106, i.e., part of the torque transmitted from the motor 106 to the engine 100, and part of the regenerative torque of the motor 107, i.e., part of the torque transmitted from the motor 107 to the engine 100, cancel out each other.
The hybrid vehicle which incorporates the power transmitting apparatus shown in FIG. 6 can travel at different transmission ratios with the engine 100 used as the propulsion source, or can travel in the EV mode with the motor used as the propulsion source. If necessary, it is possible to add the assistive propulsive power from the motor to the propulsive power from the engine 100 by, for example, making the electric power consumed by the motor 106 which produces the propulsive power greater than the electric power generated by the motor 107 which operates in the regenerative mode, or to charge the power supply for the motor by, for example, making the electric power generated by the motor 107 greater than the electric power consumed by the motor 106.
Generally, a motor that needs to produce a large torque requires itself, a drive circuit therefor, and a power supply (electric energy storage unit) therefor to have large capacities, and hence to have large sizes, large weights, and high costs. For this reason, it is desired for motors mounted on a hybrid vehicle to produce as small a torque as possible. It is also desired for a hybrid vehicle to be able to transmit substantially the same drive power as required on ordinary automobiles to the drive wheels thereof.
The conventional power transmitting apparatus described above fails to meet the above requirements, and there has been a demand for an improvement in the conventional power transmitting apparatus.
Specifically, the conventional power transmitting apparatus shown in FIG. 6 makes it difficult to substantially increase the speed reduction ratio xcex1 of the power distributor 101, for example, up to a speed reduction ratio corresponding to the low gear position of an ordinary automobile. If the speed reduction ratio xcex1 of the power distributor 101 is increased, then when the engine 100 suffers a failure and is brought to a stop, the rotatable shaft 106a of the motor 106 is rotated at a high speed by the output shaft 101b of the power distributor 101, operating the motor 106 in the regenerative mode. Because the voltage of the electric energy generated by the motor 106 is high, the capacity of the drive circuit for the motor 106 needs to be larger than would be required for the normal operation of the vehicle to meet fail-safe requirements. A bearing mechanism for supporting the rotatable shaft 106a also needs to be highly durable and expensive for allowing the shaft 106a to rotate at high speeds. One solution would be to provide a clutch between the motor 106 and the power distributor 101 and disengage the clutch upon a failure of the engine 100. However, the large-capacity drive circuit and the durable and expensive bearing mechanism are still required because the rotatable shaft 106a rotates at a high speed until the clutch is disengaged upon a failure of the engine 100.
With the conventional power transmitting apparatus shown in FIG. 6, therefore, it is difficult to substantially increase the speed reduction ratio xcex1 of the power distributor 101. The speed reduction ratio xcex1 is set to a speed reduction ratio corresponding to the second gear position, for example, of an ordinary automobile.
Since the speed reduction ratio xcex1 cannot substantially be increased, as described above, when the vehicle travels at different transmission ratios with the engine 100 used as the propulsion source, only the output power of the engine 100 is not sufficient as the drive power of the vehicle in a low vehicle speed range which requires a large propulsive power level. In such a case, the vehicle needs the assistive propulsive power from the motor 106. As a result, the torque to be provided by the motor 106 needs to be large, making it difficult to reduce the capacity of the motor 106 and the capacity of its drive circuit. In addition, it is also difficult to reduce the capacity of the power supply (electric energy storage unit) for the motors 106, 107 as situations where the electric energy stored by the power supply is consumed in the low vehicle speed range are highly likely to occur.
With the conventional power transmitting apparatus shown in FIG. 6, when the vehicle travels in the EV mode with the motor used as the propulsion source and the engine 100 at rest, part of the propulsive torque generated at the motor 106 and part of the regenerative torque generated at the motor 107 cancel out each other because the torque of the output shaft 100a is controlled to be xe2x80x9c0xe2x80x9d. Consequently, the efficiency with which to transmit the drive power from the motor 106 to the drive wheels of the vehicle is poor, and the propulsive torque of the motor 106 and the regenerative torque of the motor 107 for obtaining the desired propulsive power for the vehicle are large. Furthermore, when the engine 100 is to be started while the vehicle is running in the EV mode, the propulsive torque required by the motor 106 is required to be large because of the need for the torque to start the engine 100. As a result, it is difficult to reduce the capacities of the motors 106, 107 and their drive circuits.
The conventional power transmitting apparatus shown in FIG. 6 also allows the vehicle to be started with the output of the engine 100. When the vehicle is to be started, i.e., in a situation where the vehicle speed is xe2x80x9c0xe2x80x9d and the rotational speeds of the output shafts 101b, 102b of the power distributors 101, 102 are xe2x80x9c0xe2x80x9d, both the motors 106, 107 operate in the regenerative mode, converting the mechanical output energy of the engine 100 into electric energy. Therefore, the regenerated electric power of the motors 106, 107 is large. Consequently, it is difficult to reduce the capacities of the motors 106, 107 and their drive circuits and the capacities of the power supplies of the motors 106, 107.
As described above, with the conventional power transmitting apparatus shown in FIG. 6, it is difficult to reduce the capacities of the motors 106, 107 and their drive circuits and the capacities of the power supplies (electric energy storage units) of the motors 106, 107 while maintaining the running performance required by the vehicle.
It is therefore an object of the present invention to provide a power transmitting apparatus for a hybrid vehicle which makes it possible to reduce the capacities of motors and their drive circuits and the capacities of power supplies of the motors while maintaining the running performance required by the hybrid vehicle, and a method of controlling such a power transmitting apparatus.
To achieve the above object, there is provided in accordance with the present invention a power transmitting apparatus for a hybrid vehicle, comprising first and second power distributors having respective input shafts for receiving a rotational drive power transmitted from an engine, a power output shaft for outputting the rotational drive power transmitted from an output shaft of the first power distributor and an output shaft of the second power distributor, to drive wheels of the hybrid vehicle, a first motor for applying a propulsive torque or a regenerative torque to another output shaft of the first power distributor, a second motor for applying a propulsive torque or a regenerative torque to another output shaft of the second power distributor, a first rotation transmitting system for transmitting rotation from the engine through the first power distributor to the power output shaft, a second rotation transmitting system for transmitting rotation from the engine through the second power distributor to the power output shaft, the first rotation transmitting system having a speed reduction ratio greater than a speed reduction ratio of the second rotation transmitting system, rotation transmitting means for transmitting a torque of the second motor to the power output shaft at a speed reduction ratio greater than the speed reduction ratio of the first rotation transmitting system, and first clutch means for selectively connecting a rotatable shaft of the second motor to the rotation transmitting means and the other output shaft of the second power distributor.
The speed reduction ratio of the rotation transmitting means, the speed reduction ratio of the first power transmitting system, and the speed reduction ratio of the second power transmitting system are represented respectively by xcex11, xcex12, xcex13 (xcex11 greater than xcex12 greater than xcex13).
When the rotatable shaft of the second motor is connected to the other output shaft of the second power distributor by the first clutch means, the power transmitting apparatus operates basically in the same manner as with the conventional power transmitting apparatus shown in FIG. 6. For example, when the hybrid vehicle is propelled by the engine as the propulsion source, the first motor is controlled to operate in the propulsive mode and the second motor is controlled to operate in the regenerative mode. The hybrid vehicle is now propelled at a transmission ratio between the speed reduction ratio xcex12 of the first rotation transmitting system and the speed reduction ratio xcex13 of the second rotation transmitting system.
When the rotatable shaft of the second motor is connected to the rotation transmitting means by the first clutch means, the first motor is controlled to operate in the regenerative mode and the second motor is controlled to operate in the propulsive mode, propelling the hybrid vehicle with the engine as the propulsion source at a transmission ratio between the speed reduction ratio xcex12 of the first rotation transmitting system and the speed reduction ratio xcex11 of the rotation transmitting means. It is also possible to transmit the drive power of the second motor via the rotation transmitting means with the large speed reduction ratio xcex11 to the power output shaft for thereby propelling the hybrid vehicle. In a low speed range of the hybrid vehicle, even if the torques generated by the first and second motors are relatively low, it is possible to transmit a relatively large drive power to the power output shaft and then from the power output shaft to the drive wheels of the hybrid vehicle.
According to the present invention, therefore, it is possible to reduce the capacities of the motors, drive circuits thereof, and a power supply thereof while maintaining the required running performance of the hybrid vehicle.
Since the speed reduction ratio achieved with the rotatable shaft of the second motor being connected to the second power distributor by the first cluch means is smaller than the speed reduction ratio achieved with the rotatable shaft of the second motor being connected to the rotation transmitting means, the rotatable shaft of the second motor is disconnected from the rotation transmitting means and is connected to the second power distributor in a high speed range of the hybrid vehicle. Therefore, even if the engine fails and is stopped while the hybrid vehicle is being propelled by the engine used as the propulsion source, the rotatable shafts of the first and second motors are not rotated at a high speed.
Preferably, the power transmitting apparatus further comprises second clutch means for selectively connecting a rotatable shaft of the first motor to an output shaft of the engine and the other output shaft of the first power distributor.
When the rotatable shaft of the first motor is connected to the first power distributor by the second clutch means, the hybrid vehicle is propelled as described above. When the rotatable shaft of the first motor is connected to the output shaft of the engine by the second clutch means and the rotatable shaft of the second motor is connected to the rotation transmitting means by the first clutch means, the drive power of the second motor is transmitted via the rotation transmitting means directly to the power output shaft and then to the drive wheels of the hybrid vehicle, thus propelling the hybrid vehicle with only the drive power of the second motor (EV mode). At the same time, the drive power of the engine is directly applied to the second motor to operate the second motor in a regenerative mode, thus operating the hybrid vehicle as a so-called series type hybrid vehicle (series-operated mode). At this time, the drive power of the second motor can be transmitted directly to the engine to start the engine. Therefore, the series-operated mode can intermittently be performed.
In the EV mode, the propulsive torque of the second motor is not transmitted to the first motor and the engine, but transmitted to the drive wheels of the hybrid vehicle via the rotation transmitting means having the large speed reduction ratio xcex11. Consequently, the hybrid vehicle can travel in the EV mode efficiently with the relatively small propulsive torque of the first motor. When the second motor operates in the regenerative mode, since the output of the engine can be applied directly to the second motor, the second motor can operate efficiently in the regenerative mode. For starting the engine with the second motor, since the drive power of the second motor is transmitted to only the engine, the engine can be started with the relatively small propulsive torque. As a result, the hybrid vehicle can travel efficiently (including the series-operated mode).
According to the present invention, there is also provided a method of controlling the power transmitting apparatus with the first clutch means as described above. According to a first aspect of the present invention, to propel the hybrid vehicle with the engine used as a propulsion source thereof while operating the power transmitting apparatus at a transmission ratio between the speed reduction ratio xcex13 of the second rotation transmitting system and the speed reduction ratio xcex11 of the rotation transmitting means, the method comprises the steps of, while the hybrid vehicle is being propelled at a transmission ratio between the speed reduction ratio xcex11 of the rotation transmitting means and the speed reduction ratio xcex12 of the first rotation transmitting system, controlling the first clutch means to connect the rotatable shaft of the second motor to the rotation transmitting means, and controlling the first motor and the second motor to operate in a regenerative mode and a propulsive mode, respectively, and, while the hybrid vehicle is being propelled at a transmission ratio between the speed reduction ratio xcex12 of the first rotation transmitting system and the speed reduction ratio xcex13 of the second rotation transmitting system, controlling the first clutch means to connect the rotatable shaft of the second motor to the other output shaft of the second power distributor, and controlling the first motor and the second motor to operate in a propulsive mode and a regenerative mode, respectively.
If the power transmitting means has the second clutch means, then the second clutch means is controlled to connect the rotatable shaft of the first motor to the other output shaft of the first power distributor regardless of the transmission ratio at which the hybrid vehicle is traveling.
By thus controlling the first and second clutch means and the first and second motors, when the hybrid vehicle is propelled at a transmission ratio by the engine used as the propulsion source, a propulsive power required for the hybrid vehicle is maintained to propel the hybrid vehicle smoothly without the need for large torques generated at the first and second motors.
According to the first aspect of the present invention, furthermore, upon transition from one of the transmission ratio between the speed reduction ratio xcex11 of the rotation transmitting means and the speed reduction ratio xcex12 of the first rotation transmitting system and the transmission ratio between the speed reduction ratio xcex12 of the first rotation transmitting system and the speed reduction ratio xcex13 of the second rotation transmitting system to the other, the method preferably comprises the steps of temporarily controlling a rotational speed of the first motor at substantially zero, and controlling the first clutch to disconnect the rotatable shaft of the second motor from both the other output shaft of the second power distributor and the rotation transmitting means, and adjusting a rotational speed of the second motor. If the power transmitting means has the second clutch means, then the second clutch means is controlled to connect the rotatable shaft of the first motor to the other output shaft of the first power distributor upon transition between the transmission ratios.
Specifically, upon transition from one of the transmission ratio between the speed reduction ratios xcex11, xcex12 and the transmission ratio between the speed reduction ratios xcex12, xcex13 to the other, since the rotational speed of the second motor generally tends to vary discontinuously across the transition, the rotatable shaft of the second motor is disconnected from both the other output shaft of the second power distributor and the rotation transmitting means, and the rotational speed of the second motor is adjusted. At this time, the rotational speed of the first motor is controlled at substantially zero, bringing the transmission ratio (speed reduction ratio) of the system ranging from the engine to the power output shaft into conformity with the speed reduction ratio xcex12 at the boundary between the transmission ratio between the speed reduction ratios xcex11, xcex12 and the transmission ratio between the speed reduction ratios xcex12, xcex13. By thus performing the above control process, the transition between the above transmission ratios can smoothly be carried out without causing behavioral changes of the hybrid vehicle.
According to a second aspect of the present invention, a method of controlling the power transmitting apparatus comprises the steps of, for starting the hybrid vehicle, cutting off a current supplied to the first motor, controlling the first clutch means to connect the rotatable shaft of the second motor to the rotation transmitting means, and controlling the second motor to operate in a propulsive mode.
If the power transmitting apparatus has the second clutch means, then for starting the hybrid vehicle, the second clutch means is controlled to disconnect the rotatable shaft of the first motor from at least the other output shaft of the first power distributor, and the first clutch means is controlled to connect the rotatable shaft of the second motor to the rotation transmitting means, and the second motor is controlled to operate in the propulsive mode.
Therefore, irrespective of whether the engine is operating or not, the propulsive torque of the second motor is transmitted directly to the drive wheels of the hybrid vehicle to start the hybrid vehicle. Inasmuch as the propulsive torque of the second motor is efficiently transmitted directly to the drive wheels of the hybrid vehicle via the rotation transmitting means having the large speed reduction ratio xcex11, the hybrid vehicle can be started smoothly even if the propulsive torque of the second motor is relatively small. The capacity of the second motor can thus be reduced.
According to a third aspect of the present invention, there is provided a method of controlling the power transmitting apparatus having the second clutch means. To propel the hybrid vehicle at a predetermined vehicle speed or lower with one of the motors used as a propulsion source thereof, the method comprises the steps of controlling the second motor to operate in a propulsive mode, controlling the first clutch means to connect the rotatable shaft of the second motor to the rotation transmitting means, and controlling the second clutch means to disconnect the rotatable shaft of the first motor from at least the other output shaft of the first power distributor.
With the above method, the propulsive torque of the second motor is efficiently transmitted directly to the drive wheels of the hybrid vehicle to operate the hybrid vehicle in the EV mode. By operating the hybrid vehicle in the EV mode in a relatively low speed range lower than a given vehicle speed, the propulsive torque required for the second motor and the rotational speed of the rotatable shaft of the second motor are held to low levels.
According to the third aspect of the present invention, the method preferably further comprises the steps of controlling the second clutch means to connect the rotatable shaft of the first motor to the output shaft of the engine, and controlling the first motor to operate in a regenerative mode while operating the engine.
Alternatively, the method preferably further comprises the steps of controlling the second clutch means to connect the rotatable shaft of the first motor to the output shaft of the engine, intermittently operating the engine, controlling the first motor to operate in a regenerative mode while the engine is operating, and for starting the engine from a stop, controlling the first motor in a propulsive mode to start the engine with a drive power of the first motor.
With the above arrangement, as described above, the first motor can efficiently be operated in the regenerative mode by the output of the engine to operate the hybrid vehicle in the series-operated mode or operate the hybrid vehicle intermittently in the series-operated mode, independently of the travel of the hybrid vehicle with the propulsive torque of the second motor. If the hybrid vehicle operates intermittently in the series-operated mode, when the engine is started by the first motor, since the first motor is not required to produce a large propulsive torque, the capacity of the first motor can be reduced.
As described above, the method of controlling the power transmitting apparatus for the hybrid vehicle according to the present invention is able to efficiently operate the hybrid vehicle in various modes without the need for large torques of the first and second motors, so that the capacities of the motors, drive circuits thereof, and a power supply thereof can be reduced.
In view of the energy efficiency of the engine, the mode in which the hybrid vehicle is propelled at transmission ratios by the engine used as the propulsion source should preferably take place in a high vehicle speed range in which the vehicle speed is relatively high or in a situation where the required propulsive power for the hybrid vehicle is relatively large. The EV mode (including the series-operated mode) should preferably occur in a relatively low vehicle speed range or in a situation where the required propulsive power for the hybrid vehicle is relatively small.
The above and other objects, features, and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate a preferred embodiment of the present invention by way of example.